1. Field of the Invention
This invention pertains to holdback bars, and more particularly to hydraulic holdback bars.
2. Description of the Prior Art
Catapult assisted launches of aircraft from modern aircraft carrier decks or other short runways require that the aircraft be restrained against engine thrust and catapult force as the engines are brought up to full take off power and as the pressure in the catapult is increased to that pressure required for a safe launch. The holdback bar must release the aircraft when a pre-determined combined force has been reached, and the holdback bar should be immediately reusable for additional launches of other aircraft.
Prior holdback bars are typified by U.S. Pat. No. 3,578,273 to Thomas P. Mulgrave, dated May 11, 1971, and U.S. Pat. No. 3,813,065 to Harold W. Hallesy et al. dated May 28, 1974. In Hallesy et al. a mechanical holdback bar utilizes a locking ring and other structure to trigger release at a pre-determined combined aircraft engine thrust and catapult force level.
Mulgrave discloses a hydraulic holdback bar utilizing a plunger and housing to compress a fluid, and a spring loaded ball valve for releasing the pressurized fluid at the point when force from fluid pressure acting over the area of the ball exceeds the spring force holding the ball in the closed position. Fluid escaping from the pressure chamber flows through the valve to a receiving chamber and enables relative movement between the housing and plunger to trigger release of the aircraft. The spring loaded ball valve disclosed operates as a pressure regulator, and only permits fluid to escape the pressure chamber so long as the pressure in that chamber exceeds a pre-determined amount.
Other holdback bars utilize a tensile failure member which is expended during a single launch and which must be replaced for each additional launch. A supply of tensile links must be maintained on the flight deck for use in launching operations, and pieces of expended links may clutter the deck area. Such expended links may pose a clutter hazard to personnel and could be ingested by operating jet engines, resulting in severe engine damage. Also, time and labor is required after each launch to replace the expended tensile link. Tensile failure holdback bars also provide an instantaneous release which causes very high stresses in the nose gear and related aircraft structure.